Compound photoelectric conversion elements having a semiconductor thin film as a light absorbing layer have been developed. In particular, photoelectric conversion elements having, as a light absorbing layer, a p-type semiconductor layer with a chalcopyrite structure have high conversion efficiency and thus promising applications. Specifically, photoelectric conversion elements having a light absorbing layer of Cu(In,Ga)Se2 as a Cu—In—Ga—Se (CIGS) compound have relatively high conversion efficiency. The conversion efficiency η is expressed by η=Voc·Jsc·FF/P·100, wherein Voc is open circuit voltage, Jsc is short-circuit current density, FF is fill factor, and P is incident power density.
A photoelectric conversion element has a p-type semiconductor layer of Cu—In—Ga—Se as a light absorbing layer. Such a photoelectric conversion element generally has a structure including a blue sheet glass substrate, and a Mo back electrode, a p-type semiconductor layer, an n-type semiconductor layer, an insulating layer, a transparent electrode, an upper electrode, and an anti-reflection film, which are stacked on the substrate. A high-efficiency CIGS solar cell has a p-type semiconductor layer of CIGS and an n-type semiconductor layer of CdS, which form a pn junction. Unfortunately, such a solar cell is not considered to provide sufficient performance due to its heterojunction structure and light absorption at the n-CdS layer. A technique proposed to avoid such a problem is a homojunction structure having, instead of the n-CdS layer, a layer manufactured by n-type doping of part of a p-CIGS layer in the vicinity of a transparent electrode. However, n-type doping of a highly-crystalline p-CIGS layer is difficult. On the other hand, doping of a p-CIGS layer with low crystallinity is easy, but as its crystallinity decreases, bulk recombination occurs to reduce the cell efficiency.